This invention relates generally to shaft alignment systems. More particularly, this invention relates to methods for aligning coupled or uncoupled shafts utilizing a shaft alignment system.
As is well known, whenever two rotating machine shafts are coupled together, such as the shaft of an electric motor and the shaft of a pump, it is important that the shafts be aligned within tolerances. Such shafts, when in perfect alignment, have their extended center lines (axes of rotation) coinciding along a straight line. Misalignment can lead to vibration, excessive wear, and ultimate destruction of couplings, bearings, seals, gears and other components.
A number of shaft alignment methods is known, which generally have in common the use of suitable alignment fixtures, also termed alignment brackets. The alignment brackets are employed to measure particular relative displacements (also termed angularities and offsets) as the shafts or alignment brackets are rotated together through one revolution, taking readings at various angular positions.
It is not uncommon for the couplings, which are used to couple the two shafts to one another, to exhibit looseness or torsional play, also termed backlash. Typically the mechanical response exhibited by the mechanical coupling differs depending on which direction the coupled shafts are rotated. Current shaft alignment methodologies do not take into account the backlash effect or do so marginally.
Because of disadvantages existing with respect to prior art shaft alignment methodologies, there exists a need in the art for improved shaft alignment methodologies which include consideration of backlash effects, resulting in greater accuracy when collecting alignment data for determining shaft misalignment.
The needs expressed above, and other needs, are met by a method for acquiring data as to centerlines of first and second in-line shafts utilizing a shaft alignment system including an analyzer having a memory. The shaft alignment system includes at least one sensor head mounted on the first shaft at an initial angular position relative to the centerline of the first shaft. The sensor head includes a microprocessor having memory, a collimated light source emitter for transmitting a collimated light beam in a first direction corresponding to the centerline of the first shaft, a detector having a detecting surface for detecting a collimated light source from a second direction corresponding to a position of the centerline of the second shaft, and an angular position sensor for determining an angular position of the sensor head as the head is rotated about the centerline of the first shaft. The method first initializes the sensor head to begin acquiring data. The sensor head is then rotated in a first or a second rotational direction relative to the centerline of the first shaft while detecting an impinging collimated light beam from the second direction on the detecting surface of the detector. Based on the detecting step, positional information is acquired corresponding to the positions of the centerlines of the first and second shafts as the collimated beam impinges on the detecting surface of the detector. Angular positions of the sensor head are determined relative to the centerline of the first shaft and either the first or the second rotational direction is defined as the acquisition direction. Positional information is committed to the memory of the microprocessor only if the positional information was acquired when the head was rotating in the acquisition direction.
In an alternative embodiment, the invention utilizes a method for acquiring data as to centerlines of first and second in-line shafts. A first sensor head is mounted on the first shaft including a collimated light source emitter for transmitting a collimated light beam in a first direction corresponding to the centerline of the first shaft, a detector having a detecting surface including a first detection region and a second detection region for detecting a collimated light source from a second direction corresponding to a position of the centerline of the second shaft, and an angular position sensor for determining an angular position of the sensor head as the head is rotated about the centerline of the first shaft. A second sensor head is mounted on the second shaft including a collimated light source emitter for transmitting a collimated light beam in the second direction corresponding to the centerline of the second shaft, a detector having a detecting surface including a first detection region and a second detection region for detecting a collimated light source from the first direction corresponding to a position of the centerline of the first shaft, and an angular position sensor for determining an angular position of the sensor head as the head is rotated about the centerline of the second shaft. The first sensor head is adjusted relative to the centerline of the first shaft such that the collimated light source from the second direction impinges upon the detecting surface of the first sensor head detector. Likewise, the second sensor head is adjusted relative to the centerline of the first shaft such that the collimated light source from the first direction impinges upon the detecting surface of the second sensor head detector. The first or the second sensor head is then rotated in a first or a second rotational direction relative to the centerline of either the first or the second shaft. An impinging collimated light beam is detected from the second direction on the detecting surface of the detector of the first sensor head. Similarly, an impinging collimated light beam is detected from the first direction on the detecting surface of the detector of the second sensor head. Based on the detecting steps, positional information is acquired corresponding to the positions of the centerlines of the first and second shafts as either the first or the second collimated beam impinges on the detecting surfaces of the detectors of the first or second heads. Angular positions of the first and second sensor heads are determined relative to the centerlines of the first and second shafts, respectively. Positional information is acquired as the first and second collimated beams of light impinge on the detecting surfaces of the detectors of the sensor heads. The positional information is committed to the respective sensor head memory only if the positional information was acquired when the respective collimated light beam impinged on the respective first detection region of the detecting surface of the detector of the first or second sensor head.